A member of the respected Independent Group has cast doubt on a key assumption that the initial turnback by Malaysia Airlines Flight MH370 was manually flown.
IG member Victor Iannello says in a new blog post that more precise tracking data has given new insights into how the Boeing 777 was flown just before the transponder was disabled near a Waypoint called IGARI.
The new data was transmitted by the aircraft’s Automatic Dependent Surveillance-Broadcast system and was received by a Malaysian ground station as often as once every 30 seconds.
ADS-B broadcasts information such as position, speed and altitude with greater accuracy than traditional primary radar systems.
According to Iannello, the data shows MH370 was on track to pass over IGARI but began to turn towards the next waypoint, BITOD, before reaching it.
He calculates that the radius of the turn indicated the bank angle was about 15 degrees and notes the start of the turn and the bank angle are both consistent with the auto-pilot commanding the turn using the lateral navigation (LNAV) mode for a flight to IGARI and then BITOD.
“This suggests that at the time the transponder was disabled after 17:20:34.55, the autopilot was still engaged and the aircraft was flying in accordance with the flight plan,’’ he says, adding the Malaysian investigation report states the Mode S transponder symbol dropped off the radar display at 17:20:36.
“This is evidence that the deviation from the flight plan occurred after the transponder was disabled.”
Ianello says this differs from an officially-released low-resolution military radar image showing “an impossibly sharp turn to the left” towards BITOD after the aircraft passed over IGARI.
The Malaysians have never released the detailed military data and Iannello says it should be used with caution due to range limitations and potential inaccuracies.
He says simulations by the Malaysian investigators using entry and exit waypoints supplied by the military and had determined the aircraft was manually flown with a steep bank of 35 degrees.
“However, considering the suspected inaccuracies in the military data, the conclusion that the turnback was manually flown should be revisited,’’ he says.
“For instance, if the turn was begun prior to the entry waypoint, it would be possible to reach the exit waypoint at the proper time with a bank angle of 25°, which is a selectable bank angle when either of the autopilot modes “Heading Select” or “Track Select” is chosen.”
The new data also mitigates against the suggestion a third party could have been responsible for disabling the transponder on MH370.
Iannello notes the transponder can be disabled in the cockpit with a mode selector switch and believes the final ADS-B points may have captured an intermediate switch position as it was rotated towards the standby position.
He also observes there were just 64 seconds between the crew’s last radio transmission and the last ADS-B point.
“If the diversion from the flight path was caused by a third party forcing their way into the cockpit and taking control, those events would have to have occurred in 64 seconds or less,’’ Iannello says.
“It is very unlikely that this could have been achieved by a third party in such a short amount of time.”
Ianello says the new ADS-B data provides a better understanding of how the aircraft was flown to the point that the transponder was disabled that complements primary radar data from Kota Bharu.
“However, we are still missing the military radar data that would cover the 10-minute gap between these two data sets,” he says.
“That gap includes the left turn at the start of the diversion that put MH370 on a course back over Malaysia.
“It is important for Malaysia to release this closely-held military radar data so that other investigators that are working to solve this mystery can perform independent analyses of how the aircraft was flown during the turn.
“Whatever strategic reasons there might have originally been for withholding the military data are no longer relevant more than five years after the disappearance.”